RADAR systems are well known object-detection systems that employ radio waves to determine the range, altitude, direction, and/or speed of objects. For example, RADAR systems may be used to detect aircraft, ships, motor vehicles, weather formations, and/or terrain.
RADAR systems may be ground based (e.g., mounted on a platform or vehicle that is on the ground), or may be air based (e.g., mounted on an aircraft or other aerial platform). Depending upon the target that a RADAR system is interested in detecting, various different types of RADAR may be used. For example, unmanned aerial vehicles (UAVs) are well known, remotely operated platforms that may be used for many tasks. UAVs can be relatively small, allowing for relatively small landing and take-off areas, and can have a relatively small RADAR cross section (RCS) thus allowing operation in potentially dangerous areas with reduced likelihood of detection and without risking a human pilot. Such UAVs are commonly used in remote surveillance or monitoring operations, to obtain intelligence about activity in an area, or monitor the status of assets or people in a particular area. For example, UAVs may be used in intelligence gathering operations at relatively low altitudes in hostile territory. Another exemplary application of a UAV is monitoring operations, such as monitoring of a border between countries or monitoring assets like pipelines or a convoy which may be targeted by hostile parties. UAVs may be fixed wing aircraft, or rotary-wing aircraft. Furthermore, UAVs may be operated with reduced requirements for take-off and landing areas.
Interest in unmanned aerial systems for a multitude of applications has seen consistent increases in recent years. This interest, combined with the increasing availability of such systems, may lead to a future in which the risk of mid-air collisions between UAVs and other aircraft (both manned and unmanned) is increasingly likely. While measures have been taken to ease the integration of UAVs into existing airspace (e.g., improved communication between air traffic controllers, on board transponders, etc.) the limitations of currently available UAV sensors and the limitations of the remote operator's situational awareness result in a situation in which there is a lack of sufficient redundancy for collision avoidance in UAV systems. The situation worsens as the physical size of UAVs decreases and the sensor options become more limited. Furthermore, the majority of current solutions require cooperative use of transponders or other hardware installations on-board an already payload limited vehicle.